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Drug Interactions between Acid Control and Halfan

This report displays the potential drug interactions for the following 2 drugs:

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Interactions between your drugs

Moderate

famotidine halofantrine

Applies to: Acid Control (famotidine) and Halfan (halofantrine)

MONITOR: Famotidine may cause QTc prolongation. Theoretically, coadministration with other agents that can prolong the QT interval may result in additive effects and increased risk of ventricular arrhythmias including torsade de pointes and sudden death. According to the manufacturer, prolongation of the QT interval has been reported very rarely in patients with impaired renal function whose dose/dosing interval of famotidine may not have been adjusted appropriately. In general, the risk of an individual agent or a combination of these agents causing ventricular arrhythmia in association with QT prolongation is largely unpredictable but may be increased by certain underlying risk factors such as congenital long QT syndrome, cardiac disease, and electrolyte disturbances (e.g., hypokalemia, hypomagnesemia). In addition, the extent of drug-induced QT prolongation is dependent on the particular drug(s) involved and dosage(s) of the drug(s).

MANAGEMENT: Caution and clinical monitoring are recommended if famotidine is used in combination with other drugs that can prolong the QT interval. Patients should be advised to seek prompt medical attention if they experience symptoms that could indicate the occurrence of torsade de pointes such as dizziness, lightheadedness, fainting, palpitation, irregular heart rhythm, shortness of breath, or syncope.

References

  1. "Product Information. Pepcid (famotidine)." Merck & Co., Inc PROD (2002):
  2. Cerner Multum, Inc. "UK Summary of Product Characteristics." O 0
  3. Cerner Multum, Inc. "Australian Product Information." O 0

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Drug and food interactions

Major

halofantrine food

Applies to: Halfan (halofantrine)

GENERALLY AVOID: Grapefruit juice may increase the plasma concentration of halofantrine. The mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruits. After administration of 500 mg with 250 mL regular-strength grapefruit juice daily for 3 days, average halofantrine AUC increased 2.8-fold and peak plasma concentrations increased 3.2-fold, compared to water, in healthy subjects (n=12). QT interval prolongation increased from an average of 17 ms with water to 31 ms with grapefruit juice. Halofantrine, even at recommended doses, can cause dose-related prolongation of the QT interval, resulting in an elevated risk of potentially fatal ventricular arrhythmias including ventricular tachycardia and torsade de pointes.

ADJUST DOSING INTERVAL: The presence of food may increase the absorption and toxicity of halofantrine. Peak plasma concentrations increased seven-fold and AUC increased three-fold in healthy subjects when halofantrine was administered with high-fat food.

MANAGEMENT: The authors of the study recommend that grapefruit juice be avoided during halofantrine therapy. The manufacturer recommends performing an ECG before initiating halofantrine therapy and cardiac monitoring during and for 8 to 12 hours after completion of therapy. Halofantrine should be taken on an empty stomach at least 1 hour before or 2 hours after food.

References

  1. Giao PT, de Vries PJ "Pharmacokinetic interactions of antimalarial agents." Clin Pharmacokinet 40 (2001): 343-73
  2. "Product Information. Halfan (halofantrine)." GlaxoSmithKline (2003):
  3. Charbit B, Becquemont L, Lepere B, Peytavin G, Funck-Bretano C "Pharmacokinetic and pharmacodynamic interaction between grapefruit juice and halofantrine." Clin Pharmacol Ther 72 (2002): 514-23
  4. Abernethy DR, Wesche DL, Barbey JT, et al. "Stereoselective halofantrine disposition and effect: concentration-related QTc prolongation." Br J Clin Pharmacol 51 (2001): 231-7
View all 4 references

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Minor

famotidine food

Applies to: Acid Control (famotidine)

H2 antagonists may reduce the clearance of nicotine. Cimetidine, 600 mg given twice a day for two days, reduced clearance of an intravenous nicotine dose by 30%. Ranitidine, 300 mg given twice a day for two days, reduced clearance by 10%. The clinical significance of this interaction is not known. Patients should be monitored for increased nicotine effects when using the patches or gum for smoking cessation and dosage adjustments should be made as appropriate.

References

  1. Bendayan R, Sullivan JT, Shaw C, Frecker RC, Sellers EM "Effect of cimetidine and ranitidine on the hepatic and renal elimination of nicotine in humans." Eur J Clin Pharmacol 38 (1990): 165-9

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Therapeutic duplication warnings

No warnings were found for your selected drugs.

Therapeutic duplication warnings are only returned when drugs within the same group exceed the recommended therapeutic duplication maximum.

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Drug Interaction Classification

These classifications are only a guideline. The relevance of a particular drug interaction to a specific individual is difficult to determine. Always consult your healthcare provider before starting or stopping any medication.
Major Highly clinically significant. Avoid combinations; the risk of the interaction outweighs the benefit.
Moderate Moderately clinically significant. Usually avoid combinations; use it only under special circumstances.
Minor Minimally clinically significant. Minimize risk; assess risk and consider an alternative drug, take steps to circumvent the interaction risk and/or institute a monitoring plan.
Unknown No interaction information available.

Further information

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